Once-a-day sustained release opioid formulations are disclosed in U.S. Pat. Nos. 5,478,577; 5,672,360; 5,958,459; 6,103,261; 6,143,332; 5,965,161; 5,958,452 and U.S. Pat. No. 5,968,551. All documents cited herein, including the foregoing, are incorporated by reference in their entireties for all purposes.